docs: def _replace_path(self, path):
          """ Get the replacement value for a path """
          if path in self._field_to_key:
              return self._field_to_key[path]
          next_key = "#f%d" % self._next_field
          self._next_field += 1
          self._field_to_key[path] = next_key
          self._fields[next_key] = path
          return next_key